High-power amplifier package

ABSTRACT

Package assemblies for improving heat dissipation of high-power components in microwave circuits are described. A laminate that includes microwave circuitry may have cut-outs that allow high-power components to be mounted directly on a heat slug below the laminate. Electrical connections to circuitry on the laminate may be made with wire bonds. The packaging allows more flexible design and tuning of packaged microwave circuitry.

BACKGROUND Technical Field

The technology relates to packaged, high-power microwave circuitry, suchas high-power microwave amplifiers.

Discussion of the Related Art

Gallium-nitride semiconductor material has received appreciableattention in recent years because of its desirable electronic andelectro-optical properties. Gallium nitride (GaN) has a wide, directbandgap of about 3.4 eV that corresponds to the blue wavelength regionof the visible spectrum. Light-emitting diodes (LEDs) and laser diodes(LDs) based on GaN and its alloys have been developed and arecommercially available. These devices can emit visible light rangingfrom the violet to red regions of the visible spectrum.

Because of its wide bandgap, gallium nitride is more resistant toavalanche breakdown and has a higher intrinsic field strength comparedto more common semiconductor materials, such as silicon and galliumarsenide. In addition, gallium nitride is able to maintain itselectrical performance at higher temperatures as compared to othersemiconductors, such as silicon or gallium arsenide. GaN also has ahigher carrier saturation velocity compared to silicon. Additionally,GaN has a Wurtzite crystal structure, is a hard material, has a highthermal conductivity, and has a much higher melting point than otherconventional semiconductors such as silicon, germanium, and galliumarsenide. Accordingly, GaN is useful for high-speed, high-voltage,high-power, and high-power applications. For example, gallium-nitridematerials may be used as active circuit components in semiconductoramplifiers for radio-frequency (RF) communications, radar, and microwaveapplications.

SUMMARY

Packaging assemblies for high-power microwave circuits are described.According to some embodiments, a packaging assembly includes a laminatehaving microwave circuitry and cut-outs that allow direct mounting ofhigh-power components, such as GaN transistors, on a heat slug in thepackage. Wire bonds can provide connections between the high-powercomponents and microwave circuitry on the laminate. The direct mountingof the high-power components to the heat slug can provide improvedthermal dissipation, so that higher power operation may be achieved, andpermit flexibility in design of the microwave circuitry. For example,the microwave circuit's design may be iterated more rapidly andcomponents may be exchanged in a partially assembled package to tune thecircuit to a particular application, all without affecting or exchangingthe high-power components.

Some embodiments relate to a high-power microwave circuit assembled in apackage comprising a microwave circuit formed on a laminate, a casesupporting conductive leads that are connected to the microwave circuit,and a heat slug connected to the case and extending from an interiorregion of the case to an exterior region of the case. There may be oneor more cut-outs in the laminate. A first power transistor may bemounted directly on the heat slug within a cut-out of the laminate andconnected to the microwave circuit.

Some embodiments relate to a method of assembling a high-power amplifierin a package. The method may comprise a combination of acts including,but not limited to: mounting a power transistor on a heat slug;separately placing a laminate with a microwave circuit over the heatslug, wherein the power transistor is located within a cut-out in thelaminate; electrically connecting terminals of the power transistor tothe microwave circuit with interconnects that extend through the cut-outto the microwave circuit; and forming a case that connects to the heatslug and encloses the microwave circuit.

Various configurations of high-power amplifier packages may beimplemented. Some configurations include, but are not limited to, thefollowing embodiments.

A high-power microwave circuit assembled in a package comprising: amicrowave circuit formed on a laminate; a case supporting conductiveleads that are connected to the microwave circuit; a heat slug connectedto the case and extending from an interior region of the case to anexterior region of the case; a cut-out in the laminate; and a firstpower transistor mounted directly on the heat slug within the cut-out ofthe laminate and connected to the microwave circuit.

A high-power amplifier circuit, wherein the first power transistor iscapable of outputting power levels between 50 W and 100 W at duty cyclesgreater than 50% without significant degradation of the amplifier'sperformance.

A high-power amplifier circuit, wherein the first power transistor iscapable of outputting power levels between 100 W and 200 W at dutycycles greater than 50% without significant degradation of theamplifier's performance.

A high-power amplifier circuit, wherein the first power transistorcomprises GaN.

A high-power amplifier circuit, further comprising a second powertransistor mounted directly on the heat slug in a second cut-out in thelaminate and having an output connected to an input of the first powertransistor.

A high-power amplifier circuit, further comprising a second powertransistor mounted directly on the heat slug in a second cut-out in thelaminate and connected in parallel with the first power transistor in aDoherty configuration.

A high-power amplifier circuit, wherein the package complies withspecifications for a standardized package.

A high-power amplifier circuit, wherein the microwave circuit comprisesconductive interconnects, at least one resistor, and at least threecapacitors.

A high-power amplifier circuit, wherein the laminate is mounted directlyon the heat slug.

A high-power amplifier circuit, further comprising first wire bondsconnecting terminals of the first power transistor to the microwavecircuit.

A high-power amplifier circuit, wherein there is more than one wire bondconnecting in parallel one terminal of the first power transistor to themicrowave circuit.

A high-power amplifier circuit, further comprising second wire bondsthat connect the conductive leads to the microwave circuit, wherein thesecond wire bonds are of the same diameter as the first wire bonds andconnected in the same way as the first wire bonds.

A high-power amplifier circuit, wherein a height differential betweenbonding pads on the first power transistor and conductive interconnectson the microwave circuit is between approximately 5 mils andapproximately 20 mils.

A high-power amplifier circuit, further comprising a capacitor having abreakdown voltage between 200V and 500V mounted on the laminate.

A high-power amplifier circuit, further comprising an inductor patternedin the laminate.

Various methods for making high-power amplifier packages may bepracticed. Method embodiments may include, but not be limited to, one ormore of the following acts suitably combined.

A method of assembling a high-power amplifier in a package comprisingacts of: mounting a power transistor on a heat slug; separately placinga laminate with a microwave circuit over the heat slug, wherein thepower transistor is located within a cut-out in the laminate;electrically connecting terminals of the power transistor to themicrowave circuit with interconnects that extend through the cut-out tothe microwave circuit; and forming a case that connects to the heat slugand encloses the microwave circuit.

A method, of further comprising electrically connecting leads thatextend through the case to the microwave circuit, wherein a same processis used to electrically connect the terminals of the power transistor tothe microwave circuit and electrically connect the leads to themicrowave circuit.

A method, of, wherein the process comprises wire bonding.

A method, wherein placing the laminate over the heat slug comprisesmounting the laminate directly to the heat slug.

A method, wherein the microwave circuit includes at least one resistorand at least three capacitors.

A method, further comprising interchanging one of the at least threecapacitors for a capacitor of a different value to tune operation of thehigh-power amplifier.

A method, further comprising operating the power transistor to output apower level between 100 W and 200 W.

A method, wherein forming the case comprises forming the case to complywith specifications for a standardized package.

The foregoing apparatus and method embodiments may be included in anysuitable combination with aspects, features, and acts described above orin further detail below. These and other aspects, embodiments, andfeatures of the present teachings can be more fully understood from thefollowing description in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the figures, described herein,are for illustration purposes only. It is to be understood that in someinstances various aspects of the embodiments may be shown exaggerated orenlarged to facilitate an understanding of the embodiments. The drawingsare not necessarily to scale, emphasis instead being placed uponillustrating the principles of the teachings. In the drawings, likereference characters generally refer to like features, functionallysimilar and/or structurally similar elements throughout the variousfigures. A depicted device or circuit may be integrated within a largercircuit.

When referring to the drawings in the following detailed description,spatial references “top,” “bottom,” “upper,” “lower,” “vertical,”“horizontal,” and the like may be used. Such references are used forteaching purposes, and are not intended as absolute references forembodied devices. The terms “on” and “over” are used for ease ofexplanation relative to the illustrations, and are not intended asabsolute directional references. An embodied device may be orientedspatially in any suitable manner that may be different from theorientations shown in the drawings. The drawings are not intended tolimit the scope of the present teachings in any way.

FIG. 1 depicts one approach to dissipating heat from a packaged powertransistor;

FIG. 2A depicts a plan view of a high-power amplifier package, accordingto some embodiments;

FIG. 2B depicts an elevation view corresponding to the section line ofFIG. 2A, according to some embodiments;

FIG. 3 shows an example circuit for a two-stage, high-power amplifierpackage;

FIG. 4A depicts a structure associated with assembly of a high-poweramplifier package, according to some embodiments;

FIG. 4B depicts a structure associated with assembly of a high-poweramplifier package, according to some embodiments;

FIG. 4C depicts a structure associated with assembly of a high-poweramplifier package, according to some embodiments; and

FIG. 4D depicts a structure associated with assembly of a high-poweramplifier package, according to some embodiments.

Features and advantages of the illustrated embodiments will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings.

DETAILED DESCRIPTION

As described above, transistors comprising gallium nitride material areuseful for high-speed, high-voltage, and high-power applications becauseof the favorable material properties of gallium nitride. Someapplications relating to RF communications, radar, and microwaves canplace demanding performance requirements on devices that includegallium-nitride transistors. For example, some applications may requirehigh-power transistors capable of amplifying signals to power levelsbetween approximately 50 Watts and approximately 200 Watts.

The inventor has recognized and appreciated that at such high powerlevels, efficient thermal dissipation is needed to remove heat fromtransistors within a power amplifier package. One approach todissipating heat from a packaged power transistor is depicted in FIG. 1.The drawing depicts a power transistor 140 and electrical components 130(e.g., a capacitor, inductor, or resistor) of a circuit that is formedon a laminate 120. A plurality of thermally conductive vias 123(sometimes referred to as a “via farm”) may be formed in the laminate toimprove heat transfer from the power transistor 140 to a heat slug 107.A benefit to this approach is that the power transistor 140 may bemanufactured as a surface-mount die that may be readily mounted on thelaminate with other electrical components to form a microwave circuit.In some cases, the laminate may be soldered to a printed circuit board(PCB).

The inventor has recognized and appreciated that via farms may notprovide adequate thermal dissipation for some high-power components incertain applications. For example, where a power transistor of anamplifier outputs signals at power levels over 50 W, via farms mayinadequately dissipate heat from the transistor so that the transistor'sperformance degrades. For example, the gain linearity or drainefficiency may degrade. Additionally, the via farms may take up anappreciable area of the laminate making it difficult to mount more thantwo discrete capacitors on the laminate within the package. This canmake it difficult or impossible to implement impedance matching withinthe package for the microwave circuit.

The inventor has further recognized and appreciated that although powertransistors can be readily incorporated on a monolithic microwaveintegrated circuit (MMIC), a turn-around time for changes in a MMICdesign (e.g., to tune performance of an amplifier) can be months. Thisis because there is no way to readily retune a MMIC, so that the MMICneeds to be refabricated. However, the inventor has recognized andappreciated that turn-around times for redesign of laminate circuitrycan be days.

An improved approach to packaging high-power transistors or otherhigh-power components is depicted in FIG. 2A and FIG. 2B. According tosome embodiments, high-power components 142, 144 (such as GaNtransistors) may be mounted directly on a heat slug 107 through cut-outs125 in a laminate 120. Wire bonds 115 may be used to connect betweenterminals on the high-power components and microwave circuitry on thelaminate 120. The direct mounting of the high-power components on theheat slug can improve heat dissipation into the heat slug and allow thecomponents to operate at higher power levels than is possible forconventionally packaged, high-power devices. For example, a devicehaving direct mounting of transistors on the heat slug 107 may operateat power levels between about 50 W and about 100 W at duty cyclesgreater than 50% without appreciable performance degradation (e.g.,without appreciable degradation of gain, linearity, or drainefficiency). In some implementations, a device having direct mounting oftransistors on the heat slug 107 may operate at power levels betweenabout 100 W and about 200 W at duty cycles greater than 50% withoutappreciable performance degradation due to heating. For example, a powertransistor mounted on a laminate typically exhibits a gain reduction ofabout 0.5 dB to about 1 dB due to heating considerations for pulsed andcontinuous-wave operation compared to a transistor mounted directly on aheat slug. For a laminate-mounted transistor, there is a higher thermalresistance to the heat slug. The increased thermal resistance causes thetransistor to get hotter and limits its maximum operating temperature.Therefore, the transistor must be operated at reduced gain values (byabout 0.5 dB to about 1 dB) to avoid overheating and damaging thetransistor. Direct mounting of the transistor on the heat slug can allowhigher-power operation to recover about 0.5 dB to about 1 dB of gain.

The phrases “direct mounting” and “mounted directly on the heat slug”refer to bonding, adhering, or otherwise attaching a transistor or otherhigh-power component directly to the heat slug through a cut-out in thelaminate. In some embodiments, there may be a layer ofthermally-conductive adhesive between the high-power component and theheat slug.

In some embodiments, the high-power components 142, 144 may comprisehigh-power GaN transistors, such as a high-power, depletion-mode,high-electron-mobility transistor (HEMT), high-voltage GaN-on-Si FET,and high-voltage heterojunction bipolar transistor (HBT). In someembodiments, a transistor may be formed as a junction field-effecttransistor (JFET) or low-voltage HBT. Other transistor architectures maybe used in other embodiments. Other transistor architectures mayinclude, but not be limited to, metal-oxide-semiconductor field-effecttransistor (MOSFET) and metal-insulator-semiconductor field-effecttransistor (MISFET). In some cases, the high-power components 142, 144may be of mixed types. For example, a first stage of an amplifier maycomprise first component 142 that is a low-voltage transistor (e.g., a5V HBT) and a second stage may comprise a second component 144 that is a50V GaN-on-Si FET. In other embodiments, high-power components mayinclude, but not be limited to, high-power GaN diodes, LEDs or laserdiodes, high-power thyristors or other similar or different high-powerdevices which may or may not be formed from GaN.

As used herein, the phrase “gallium nitride material” refers to galliumnitride (GaN) and any of its alloys, such as aluminum gallium nitride(Al_(x)Ga_((1-x))N), indium gallium nitride (In_(y)Ga_((1-y))N),aluminum indium gallium nitride (Al_(x)In_(y)Ga_((1-x-y))N), galliumarsenide phosporide nitride (GaAs_(x)P_(y) N_((1-x-y))), aluminum indiumgallium arsenide phosporide nitride (Al_(x)In_(y)Ga_((1-x-y))As_(a)P_(b)N_((1-a-b))), amongst others. Typically, when present, arsenic and/orphosphorous are at low concentrations (i.e., less than 5 percent byweight). In certain preferred embodiments, the gallium nitride materialhas a high concentration of gallium and includes little or no amounts ofaluminum and/or indium. In high gallium concentration embodiments, thesum of (x+y) may be less than 0.4 in some implementations, less than 0.2in some implementations, less than 0.1 in some implementations, or evenless in other implementations. In some cases, it is preferable for atleast one gallium nitride material layer to have a composition of GaN(i.e., x=y=a=b=0). For example, an active layer in which a transistorchannel is formed may have a composition of GaN. Gallium nitridematerials may be doped n-type or p-type, or may be intrinsic. Suitablegallium nitride materials are described in U.S. Pat. No. 6,649,287,which is incorporated herein by reference in its entirety.

Referring again to FIG. 2A, a high-power package 200 may include anouter case 105, a laminate 120 mounted within the case 105 that includesmicrowave circuitry and cut-outs 125, a heat slug 107 mounted in thecase, and one or more conductive pins or leads 110 extending through thecase walls, at least some of which provide electrical connections tocircuitry on the laminate. The laminate circuitry may comprise discretecomponents 130 (e.g., resistors, diodes, capacitors, inductors, etc.)and include patterned conductive interconnects 135. In some embodiments,the laminate may comprise multiple levels of conductive interconnectsand one or more ground planes separated by dielectric material. Thelaminate may have a thickness between approximately 5 mils andapproximately 30 mils, according to some embodiments, though otherthicknesses may be used in some cases. Examples of suitable laminatesare produced by Rogers Corporation of Rogers, Conn., such as the RO3000®laminates. A suitable laminate may have a high dielectric constant(e.g., greater than 2), and be formed from a ceramic-filledpolytetrafluoroethylene (PTFE) composite, though other laminatecompositions may be used in some cases. A laminate 120 may includecut-outs 125 that provide openings through the laminate. There may beconductive interconnects or bond pads for wire bonds formed adjacent tothe cut-outs.

When the laminate is mounted within the package 200, there may be one ormore high-power components 142, 144 located within the cut-outs 125. Ahigh-power component may be formed as a semiconductor die and may bemounted directly on an underlying heat slug 107. One or more wire bondsmay be made between terminals on each high-power component and adjacentconductive interconnects or bond pads that connect to conductiveinterconnects on the laminate 120.

When using the terms “on,” “adjacent,” or “over” in to describe therelative locations of a first item and a second item (e.g., structure Ais adjacent to structure B), there may or may not be interveningmaterial between the first item and the second item. When a first itemis described as being “immediately” on, adjacent to, or over a seconditem, essentially no intervening material is present. When a first itemis described as being “on” or “over” a second item, the first item maycover the entire second item, or a portion of the second item.

The heat slug 107 may comprise any suitable material that exhibits ahigh thermal conductivity, such as copper or aluminum, though othermaterials may be used. The heat slug may extend through the case 105, sothat it can directly contact an external heat sink. In some embodiments,the package 200 may include holes or other features that allow thepackage to be screwed or otherwise securely fastened to an instrumentboard, for example, so that the heat slug 107 makes intimate contactwith a heat sink on the instrument board. In some implementations, theheat slug 107 may provide a ground plane or reference potential forcircuitry on the laminate.

The case 105 may comprise a plastic or molded epoxy in some embodiments,and the package may be formed in a standardized shape (e.g., a TO-272package, an AC-400 package, an AC-780 package etc.). FIG. 2A and FIG. 2Bdepict a decapped portion of a package. In embodiments, the case 105 mayextend or be over-molded above the laminate to enclose the laminate 120and high-power components 142, 144.

By providing cut-outs 125 in the laminate 120, mounting of thehigh-power devices 142, 144 is separated from assembly of the laminate.Typically, high-power components formed from materials other than Sicontribute higher costs to packaged high-power devices. By using alaminate in a package, some components (e.g., resistors, capacitors,inductors, impedance-matching networks, voltage bias networks, etc.) maybe formed at lower-cost (using surface-mount devices (SMDs), printedcomponents on the laminate, Si-based dies, etc.) rather than formingthem on or from a more expensive semiconductor, as might be done for aMMIC that is formed from a more costly semiconductor wafer. In someembodiments, the high-power components 142, 144 can be made small insize compared to a MMIC, and therefore reduce costs.

A further consideration is that revising a MMIC can require one orseveral months of turn-around time and loss of an expensive device. Onthe other hand, revising laminate circuitry, without integratedhigh-power components, can entail only several days of delay.Additionally, discrete components on a laminate may be changed morereadily (prior to assembly in a package or after partial assembly in apackage) to fine tune packaged devices for a particular application orfrequency range when expensive high-power devices are not integrated onthe laminate. For example, there is no risk of damaging the high-powerdevices when interchanging discrete components on the laminate.

An additional benefit of mounting the high-power components on the heatslug within the cut-outs is that the cut-outs can occupy less area thanvia farms, so that more laminate area is available forimpedance-matching and/or filtering circuitry. In some implementations,power management circuitry may be included inside the package 200.

There are also additional benefits to using a laminate 120 incombination with high-power components rather than manufacturing adevice as a MMIC. MMIC technology typically has limited breakdownvoltages (in the range of 50 V to 100 V) for integrated capacitors. Toincrease the capacitance breakdown voltage to over 200 V, thecapacitor's dielectric layer would need to become significantly thicker(e.g., at least double). Current SMD capacitors, which can be used on alaminate, can have breakdown voltages as high as 500 V. Additionally,SMD inductors or inductors 118 patterned from a conductive layer on thelaminate can exhibit appreciably higher Q values than inductors formedon a MMIC, and are of lower cost. SMD and laminate inductors can exhibitlower loss and handle higher current levels than MMIC inductors.

According to some embodiments, the laminate 120 may also be mounteddirectly on the heat slug 107, as depicted in FIG. 2B, or it may bemounted within a few mils above the heat slug. By mounting the laminatedirectly on the heat slug, a height differential between bonding pads ona high-power component 142 and conductive interconnects 135 on thelaminate is reduced. For example, the height differential may be betweenabout 5 mils and about 20 mils. This can allow a same electricalconnection process (e.g., wire or ribbon bonding) to be used for makingelectrical connections between the high-power component and microwavecircuitry on the laminate and between leads 110 and the microwavecircuitry.

A high-power component 142, 144 mounted in a package 200 may include aplurality of bond wires 115 connected to a same terminal of thecomponent, as depicted in FIG. 2A. For example, there may be more thanone bond wire connected to a gate terminal or drain terminal of a powertransistor. The wire bonds may be spaced apart on a regular pitch insome cases, or may be spaced on an irregular pitch. The pitch of bondwires 115 connected to a same terminal may be between approximately 0.1mm and approximately 0.5 mm. The bond wires may comprise gold or anyother suitable metal. In some implementations, the bond wires may beconnected to conductive interconnects or bond pads using a ball bond orwedge bond for example. In some cases, ribbon bonds may be used insteadof, or in addition to, bond wires.

According to some embodiments, a high-power amplifier package 200 mayinclude one or more impedance-matching networks and/or biasing networks.An impedance-matching network may transform input and output impedancesto and from a high-power transistor, for example, to match impedances ofadjacent circuitry to which the transistor connects. For example, animpedance-matching network connected to a gate of a power transistor maytransform the input impedance of the transistor to an impedance value(e.g., approximately 50 Ohms) that better matches an output impedance ofupstream circuitry to which the gate connects. Impedance-matchingnetworks may comprise any suitable combination of resistors, capacitors,inductors, and transmission line segments, and may be designed toapproximately match impedances at a selected operating frequency(sometimes referred to as a “fundamental frequency”) or over frequencyrange for the amplifier. An operating frequency may be betweenapproximately 500 MHz and approximately 6 GHz, according to someimplementations, or may be between approximately 1 GHz and approximately6 GHz, though some embodiments may be designed for lower or higherfrequencies. A high-power amplifier package 200 may further includecapacitive shunts and/or filters to reduce or terminate power at thesecond harmonic and/or higher harmonics of the fundamental frequency, orto suppress noise.

In some embodiments, a voltage bias network may be included in ahigh-power amplifier package 200. A voltage bias network may include aseparate negative voltage generator die, for example, that is solderedor otherwise connected to circuitry on the laminate 120. The voltagebias network may be configured to generate and provide an appropriatenegative gate bias to the GaN power transistors prior to biasing drainsof the power transistors, so as to avoid damaging the power transistors.In some embodiments, the voltage bias network may generate one or morenegative bias levels from a fixed voltage input received by the package200.

FIG. 3 depicts just one example of amplification circuitry 300 that maybe included in a high-power amplifier package 200, though the inventionis not limited only to amplifiers. According to some embodiments, ahigh-power amplifier may be a multistage amplifier having a first powertransistor PT1 and a second power transistor PT2. Wire bonds within thepackage 200 may contribute inductances L1-L6 to the circuit. Discretecapacitors C1-C12 and resistors R1, R2 (which may be surface mountcomponents) may be included in the circuit for impedance matching,biasing, and filtering. For example, resistors R1, R2 and capacitors C2,C8 may be arranged to bias the gates of transistors PT1, PT2. Shuntcapacitors C5, C6 and C11, C12 may be arranged to suppress harmonics atthe outputs of the transistors. The circuitry 300 may further includetransmission line segments 310 of selected lengths that rotate impedancevalues at gate inputs of the transistors to better match outputimpedances of upstream circuits.

The amplifier circuitry 300 may be tuned to a desired operatingfrequency or frequency range by selecting resistor and capacitorcomponent values for a particular operating frequency or frequencyrange. Inductance values may be changed by adding or removing bond wiresto bond-wire groups where two or more wire bonds are made to a sameterminal, for example. In some implementations, discrete inductors maybe included in the circuit. Transmission line segment lengths andproperties may be changed by changing a laminate design.

The tuning process for a microwave circuit may be performed with theassistance of numerical simulation or using empirical methods. Forexample, tuning may be implemented using a software tool such asAdvanced Design System (ADS) available from Keysight Technologies, Inc.of Santa Rosa, Calif. Other suitable software tools include, but are notlimited to NI AWR Design Environment available from AWR Corporation ofEl Segundo, Calif. and Sonnet® software tools available from SonnetSoftware of North Syracuse, N.Y.

Although the above structures and circuits have been described primarilyfor gallium-nitride transistors, other semiconductor materials may beused in other embodiments that use high-power, high-speed transistors orother high-power components. Some embodiments may include heterojunctiontransistors comprising SiC, SiGe, GaAs, InP, and CdTe. Direct mountingof high-power transistors on heat slugs in power-amplifier packages maybe useful for various types of amplifiers including, but not limited to,class-A, class-B, class-J, class-F, inverse class-F, class-AB, andDoherty amplifiers. For example, a Doherty amplifier configuration maybe included within the package 200 where transistors in the parallelamplification paths are mounted directly on the heat slug.

There are various processes that may be used to assemble high-poweramplifier packages, such as the package 200 depicted in FIG. 2A.Structures associated with methods for assembling a packaged high-poweramplifier are depicted in FIG. 4A to FIG. 4D.

According to some embodiments, a method for assembling a packagedhigh-power amplifier may comprise mounting a power transistor 143directly on a heat slug 107, as depicted in FIG. 4A. The powertransistor may be adhered, bonded, or otherwise placed in thermalcontact with the heat slug. The heat slug may be mounted within orotherwise connected to a case 105 in some embodiments. In otherembodiments, the case may be formed or attached around the heat slugafter the power transistor and/or laminate is/are mounted over the heatslug.

A method of assembly may comprise mounting a laminate 120 with microwavecircuitry over the heat slug, such that the power transistor 143 islocated within a cut-out 125 of the laminate, as depicted in FIG. 4B.The laminate may, or may not, contact the heat slug. Conductive leads110 may be mounted adjacent to the laminate and microwave circuitry.

A method of assembly may comprise making electrical connections betweenterminals on the power transistor 143 and the microwave circuitry, andbetween the leads 110 and the microwave circuitry, as depicted in FIG.4C. According to some embodiments, the electrical connections may bemade using a same wire-bonding process (e.g., using bond wires having asame diameter and bonded in the same manner). In some cases, a discretecomponent 130 may be replaced with a component 132 of a different value(e.g., different capacitance or different resistance) after the laminatehas been mounted to tune operation of the microwave circuitry to aparticular application (e.g., a particular operating frequency,frequency range, or gain characteristic).

A method of assembly may include enclosing the laminate and powertransistor with an upper case 106. The upper case may be bonded to thelower case 105, or may be formed by over-molding in place. In someembodiments, an interior region 410 may be filled with an insulatingmaterial, or may be filled by the upper case material.

The terms “approximately” and “about” may be used to mean within ±20% ofa target dimension in some embodiments, within ±10% of a targetdimension in some embodiments, within ±5% of a target dimension in someembodiments, and yet within ±2% of a target dimension in someembodiments. The terms “approximately” and “about” may include thetarget dimension.

The technology described herein may be embodied as a method, of which atleast some acts have been described. The acts performed as part of themethod may be ordered in any suitable way. Accordingly, embodiments maybe constructed in which acts are performed in an order different thandescribed, which may include performing some acts simultaneously, eventhough described as sequential acts in illustrative embodiments.Additionally, a method may include more acts than those described, insome embodiments, and fewer acts than those described in otherembodiments.

Having thus described at least one illustrative embodiment of theinvention, various alterations, modifications, and improvements willreadily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be within the spirit andscope of the invention. Accordingly, the foregoing description is by wayof example only and is not intended as limiting. The invention islimited only as defined in the following claims and the equivalentsthereto.

What is claimed is:
 1. A high-power amplifier circuit assembled in apackage comprising: a microwave circuit formed on a laminate; a casesupporting conductive leads that are connected to the microwave circuit;a heat slug connected to the case and extending from an interior regionof the case to an exterior region of the case; a cut-out in thelaminate; and a first power transistor mounted directly on the heat slugwithin the cut-out of the laminate and connected to the microwavecircuit.
 2. The high-power amplifier circuit of claim 1, wherein thefirst power transistor is capable of outputting power levels between 50W and 100 W at duty cycles greater than 50% without significantdegradation of the amplifier's performance.
 3. The high-power amplifiercircuit of claim 1, wherein the first power transistor is capable ofoutputting power levels between 100 W and 200 W at duty cycles greaterthan 50% without significant degradation of the amplifier's performance.4. The high-power amplifier circuit of claim 3, wherein the first powertransistor comprises GaN.
 5. The high-power amplifier circuit of claim4, further comprising a second power transistor mounted directly on theheat slug in a second cut-out in the laminate and having an outputconnected to an input of the first power transistor.
 6. The high-poweramplifier circuit of claim 4, further comprising a second powertransistor mounted directly on the heat slug in a second cut-out in thelaminate and connected in parallel with the first power transistor in aDoherty configuration.
 7. The high-power amplifier circuit of claim 3,wherein the package complies with specifications for a standardizedpackage.
 8. The high-power amplifier circuit of claim 7, wherein themicrowave circuit comprises conductive interconnects, at least oneresistor, and at least three capacitors.
 9. The high-power amplifiercircuit of claim 1, wherein the laminate is mounted directly on the heatslug.
 10. The high-power amplifier circuit of claim 9, furthercomprising first wire bonds connecting terminals of the first powertransistor to the microwave circuit.
 11. The high-power amplifiercircuit of claim 10, wherein there is more than one wire bond connectingin parallel one terminal of the first power transistor to the microwavecircuit.
 12. The high-power amplifier circuit of claim 10, furthercomprising second wire bonds that connect the conductive leads to themicrowave circuit, wherein the second wire bonds are of the samediameter as the first wire bonds and connected in the same way as thefirst wire bonds.
 13. The high-power amplifier circuit of claim 9,wherein a height differential between bonding pads on the first powertransistor and conductive interconnects on the microwave circuit isbetween approximately 5 mils and approximately 20 mils.
 14. Thehigh-power amplifier circuit of claim 1, further comprising a capacitorhaving a breakdown voltage between 200V and 500V mounted on thelaminate.
 15. The high-power amplifier circuit of claim 1, furthercomprising an inductor patterned in the laminate.
 16. A method ofassembling a high-power amplifier in a package, the method comprising:mounting a power transistor on a heat slug; separately placing alaminate with a microwave circuit over the heat slug, wherein the powertransistor is located within a cut-out in the laminate; electricallyconnecting terminals of the power transistor to the microwave circuitwith interconnects that extend through the cut-out to the microwavecircuit; and forming a case that connects to the heat slug and enclosesthe microwave circuit.
 17. The method of claim 16, further comprisingelectrically connecting leads that extend through the case to themicrowave circuit, wherein a same process is used to electricallyconnect the terminals of the power transistor to the microwave circuitand electrically connect the leads to the microwave circuit.
 18. Themethod of claim 17, wherein the process comprises wire bonding.
 19. Themethod of claim 17, wherein placing the laminate over the heat slugcomprises mounting the laminate directly to the heat slug.
 20. Themethod of claim 16, wherein the microwave circuit includes at least oneresistor and at least three capacitors.
 21. The method of claim 20,further comprising interchanging one of the at least three capacitorsfor a capacitor of a different value to tune operation of the high-poweramplifier.
 22. The method of claim 16, further comprising operating thepower transistor to output a power level between 100 W and 200 W. 23.The method of claim 16, wherein forming the case comprises forming thecase to comply with specifications for a standardized package.